For the effective use of the wind force for the propulsion of a ship from the point of view of energy saving, fitting of sails to ships is being proposed. One of the conventional sails to be fitted to the ship is a canvas sail. A sail of this kind however requires much time and labor for handling.
To solve this difficulty, a sail comprising thin metal sheets or synthetic resin sheets fitted to reinforcing ribbed members (hereinafter simply referred to as a "rigid sail") has been used in place of the above-mentioned canvas sail. This rigid sail, capable of being automatically opened and closed by a mechanical force, can solve the above-mentioned problem.
As one of such rigid sails, a rigid sail substantially identical with the rigid sails shown in FIGS. 1 to 4 is disclosed in Japanese Patent Provisional Publication No. 47,994/80 (hereinafter referred to as the "prior art"). This rigid sail is described below. In FIGS. 1 to 4, 1 is a mast equipped vertically on the deck (not shown) of a ship. 2 is a mast rotating mechanism for rotating the mast 1 around the axis thereof. This mechanism 2 comprises a gear 3 fixed on the periphery of the mast 1 in the lower portion thereof and a motor 5 having another gear 4 engaging with the above-mentioned gear 3. 6 is a rigid sail fitted to the mast 1 in parallel with the axis thereof through a plurality of fitting members 7, the rigid sail 6 comprising a central sail portion 6A fixed to the mast 1, and two sail portions 6B fitted to both ends of the central sail portion 6A so as to be pivotably movable. 8 is an opening/closing device for opening and closing each of the sail portions 6B, this device 8 comprising a movable rod 10 vertically movably fitted, through a plurality of guide members 9, to the mast 1 in parallel therewith, a lift 11 comprising, for example, a cylinder for vertically moving the movable rod 10, and a plurality of connecting rods 12 provided at prescribed intervals in a vertical row on each of the sail portions 6B, one-side ends of the connecting rods 12 being connected, through respective universal bearings 13, to each of the sail portions 6B at prescribed intervals to form a vertical row, and the other ends of the connecting rods 12 being connected, through another respective universal bearings 14, to the movable rod 10 at prescribed intervals to form a vertical row.
By driving the motor 5 of the mast rotating mechanism 2, the rigid sail 6 is rotated around the mast 1 through the gears 3 and 4. The sail portions 6B of the rigid sail 6 are opened, as shown in FIGS. 1 and 2, by raising the movable rods 10 with the lift 11, and are closed, as shown in FIGS. 3 and 4, by lowering the movable rods 10 with the lift 11.
The above-mentioned rigid sail should be easily and certainly rotated, opened and closed in response to changes in wind velocity and wind direction, but such a method has not as yet been proposed.